Since getting back from Oz I've noted my computer has developed quite a nasty case of fan noise. Having checked the Qfan and Cool & Quiet apps. to see that they're working, I just opened up my case and after a bit of dusting, "stalled-to-stop" my two 120mm case fans, the 80mm HSF fan and the 45mm fan on my 7800GTX. None of them were the culprit (idle, they're all virtually silent) - and so, as I feared, my attention was drawn to the PSU.

And so I need a "new" one - if a PSU still suitable for a 939 mobo could still be called "new". I'm not interested in modular having never seen the need and happy to bundle cables in the upper "void" area of my Akasa Eclipse case - but I given how my computer is on 24/7 - I do want the quietest going - for reasonable money that is.

But I'm a long time out of speccing computers - so advice on manufacturer/models would be greatly appreciated.

EDIT Using THIS tool - tells me I'm looking at 305-355W units, far less than the 900W Silverstone I've got, does that sound right?

If your computer is actually going to use x Watts of power, you want to look at something a reasonable amount over that, partly for efficiency, partly so your not running it under heavy load, and also because it won't generate as much heat because it's not working as hard.

I tend to use either Enermax or Corsair units in my builds, as they are both very quiet. The Enermax units are slightly more engineered towards volume (for example the fan in the PSU can be controlled using the PSU fan header on the motherboard, rather than just the PSU's temperatures, but they are a little more expensive than the Corsair units on the whole.

A 900W power supply doesn't constantly output 900W it means thats the maximu draw it can cope with, if you are drawing 355W then thats what your PSU will provide.

As for operating efficiency its not necessarily the case that running a PSU at half capacity is more efficient than running it at full load. But this depends wholey on the design and engineered parameters of a specific unit.

I would always up spec the rating slightly so as to give yourself a bit of room for manouver and the ability to upgrade other components in the future but your priority should be looking for one with the lowest Db output that meets or slightly exceeds your power requirements. remember if its designed to put out 900W its going to need a bigger fan than one thats rated lower.

Well I have my nephews old 380w Antec NeoPower modular PSU sitting on the floor in my office doing nothing.

If you were willing to collect it then its yours.

That app tells me I need a 340w PSU to run my stuff. I'm using a 300w Lite-On PSU that came in the Compaq case.

I have a 939 system running from a 480w Tagen 2Force SLI. Unfrotunately, most of the cheaper PSUs these days are noisy. So if you want quiet, you're gonna need to go for something around the 500-600w mark (budget dependant of course). My Dad's machine had the same problem a few years ago and he has the same case. We went Corsair HX 620 and it's virtually silent and has never shown any sign of problems.

I'd probably go Corsair again, but the noise thing is definitely an issue in the cheaper (yet very well built and efficient) end of the market.

+1 for Corsair. I have the HX620 and its never let me down, even when I was running an overclocked Q6600 and GTX275. I'm just not sure its all that quiet (could be my other fans to be fair) especially considering 'silent' PSUs are available.

Some of the better of the silent PSUs come at a big price too!
[url="http://www.quietpc.com/gb-en-gbp/products/psus-300-500?sort=price&descending=yes&set=Set"]
Quiet PSU[/url]

I have that Corsair HX 620 in my works machine and when it has to work hard boy is it LOUD!

Seasonic always used to make very quiet PSU's

Maybe, but I've never heard my Dad's as it's clearly not working hard to power a 939 system with one HDD and a 66GT

You're right about Seasonic of course. But they're expensive.